de witte



M r h' 1964 J. T. DE WITTE 3,126,716

' DEFROSTING WITH CIRCULATING AIR Filed Aug. :51, 1962 2 Sheets-Sheet 1 l5l 1w J 4\\\ I INVENTOR. I55 John T. DeW/Y/e Fly. 2

[TBY' 5 His Aflomey March 31, 1964 J. T. DE WITTE DEFROSTING WITH CIRCULATING AIR 2 Sheets-Sheet 2 Filed Aug. 51, 1962 INVENTOR.

John 7.' Dew/fie His Attorney United States Patent Ofiice 3,126,716 DEFROSTING WITH CIRCULATING AIR John T. De Wrtte, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Aug. 31, 1962, Ser. No. 220,710 9 Claims. (El. 62ll56) pensive and often operated more frequently than necessary.

It is an object of this invention to provide a refrigerator in which the first never collects in the storage compartments an inexpensive defrosting system which defrosts the evaporator or evaporators only when needed.

It is another object of this invention to use the thermostatic air valve in such a refrigerator having a single evaporator for cooling both above and below freezing frost-free compartments to operate dampers to provide rapid and effective defrosting through a defrost air circulation system.

It is another object of this invention to freeze the defrost water on a screen for substantially blocking the defrost air circulating system during normal refrigeration and to melt the frozen water upon the screen coincidentally with the defrosting to open the defrost air circulating system.

These and other objects are attained in the form shown in the drawings in which air from the below and above freezing compartments is circulated through the evaporator by a fan having two outlets, one discharging into the below-freezing compartment and the other discharging into the above-freezing compartment. A thermostatic air valve responsive to the temperature of the air in the above-freezing compartment controls the discharge of cold air thereto so as to maintain its temperature just above freezing for providing suitable refrigeration temperatures therein. The motor compressor unit is cycled according to temperatures of the below-freezing compartment to maintain suitable temperatures therein.

When frost builds up upon the evaporator compartment sufiiciently to contact and cool a second thermostatic switch to an abnormally low temperature, a defrost period is initiated in which the compressor motor is (file-energized and a defrost heater is energized While the fan continues to run. In addition, a small heater is energized which actuates the air valve to. a high pressure and temperature condition to close the outlet of the fan to the below-freezing compartment and to throttle the outlet of the fan to the above-freezing compartment. The fan operates at all times but during the defrost period its discharge is split so that part goes through the screen and another part is discharged to the above freezing compartment. Some cold air will therefore refrigerate the above-freezing compartment during the defrost period. The defrost heater melts the ice off a screen which opens a by-pass located in a split portion of the second outlet of the blower so that hot air recirculates through the evaporator compartment and the evaporator to quickly defrost the evaporator. This screen is normally wetted during the defrost period and the defrost water is frozen thereon by a small tubular refrigerating coil during the refrigerating period to close the by-pass at all times excepting during a defrost 3,126,716 Patented Mar. 31., 1964 period. The closing of the damper in the outlet of the fan to the below-freezing compartment is caused by the overtravel of the thermostatic air valve which during its overtravel also moves the damper to a throttling positlon.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.

In the drawings:

FIGURE 1 is a side vertical sectional view partly diagrammatic of a two-compartment refrigerator embodying one form of my invention;

FIGURE 2 is a plan view of the screen together with the defroster heater and the refrigerant tube used respectively to melt and freeze the defrost water on the screen;

FIGURE 3 is a view in elevation with the doors open showing the air circulating and control system for both compartments;

FIGURE 4 is an enlarged sectional view partly diagrammatic taken along the lines 4-4 of FIGURE 3;

FIGURE 5 is a wiring diagram for the apparatus; and

FIGURE 6 is a diagram of the refrigerating system for the refrigerator shown in FIGURES 1 to 4.

Referring now to the drawings and more particularly to FIGURE 1, there is shown a refrigerator cabinet 20 provided with upper and lower insulated doors 22 and 24 providing direct access to the below-freezing compartment 26 and the above-freezing compartment 28 which are enclosed within the insulated Walls 30. The

below-freezing compartment 26 is enclosed by a metal liner 32 upon the bottom of which rests a transverse finned evaporator 34. Resting upon the top of this evaporator 34 is a sheet metal false wall 36 forming between it and the bottom wall 38 an evaporator compartment 40 containing the evaporator 34. The evaporator compartment 40 has a front entrance 42 through which air from the below-freezing compartment 26 may enter and a second or bottom entrance 44 through which air may be received from the above-freezing compartment 28 through the opening 46 and the passage 48 in the rear wall as well as the passage 56 in the top wall thereof. Insulation 52 is provided between the top wall of the above-freezing compartment 28 and the passage 50.

At the rear of the evaporator compartment 40 there is provided a shroud 54 which conducts the air through the inlet 56 to the centrifugal fan 58. This fan 58 is driven by the electric motor 66 located in the rear wall 62 of a refrigerator 26. The fan 58 is provided with one upwardly extending discharge outlet 64 which discharges into the upper portion of the below-freezing compartment 56. It is also provided with a downwardly extending discharge outlet 66 which connects through the passage 68 and the opening 70 with the abovefreezing compartment 28. This downwardly extending discharge outlet 66, however, is divided or split by a partition wall 72 which connects with an opening normally closed by a screen 74 into the passage 50 so as to provide a bypass for the air permitting the air to flow from the fan 58 to the passage 50. To prevent the air in the above-freezing compartment from being cooled below freezing temperatures, there is provided in the passage 68 a butterfly damper 76 controlled thermostatically in accordance with the temperature of a thermostat bulb 78 located adjacent the outlet 46 from the above-freezing compartment 28 to the passage 48 so that the bulb 78 is responsive to the temperature of the air in the compartment 28.

The thermostat bulb '78 contains a volatile liquid which creates a pressure which is responsive to the temperature of the above-freezing compartment 28. This bulb 78 transmits through the tube 80 the pressure to a fluid motor 82 which includes an outer casing and an inner bellows. The inner bellows has its upper closed movable end connected to the bellows follower 84 which in turn connects through a spring loaded lost motion connection 86 and a threaded adjustable connection 88 with the actuating wire 98 connecting directly to the butterfly type damper 76 which is pivoted within the horizontal tube portion 92. The lost motion connection includes a transverse pin extending through lost motion slots on the opposite sides thereof in the upper portion of the connection 88 as well as a light compression spring acting between the parts 84 and 88 to extend yieldingly the lost motion connection to its maximum extent. A spring retainer 96 supports the lower end of the compression spring 94 which extends upwardly to an upper spring retainer provided upon the bellows follower 84 so that "it allows increasing downward movement of the bellows follower 84 as the pressure increases within the fluid motor 82. The screw adjustment 88 is provided with a "narrow actuating disk 98 which, in the open position, is

adapted to rest upon and engage a small, short compression-type coil spring 121 which serves as a resilient stop to resiliently oppose the movement of the butterfly damper 76 beyond the fully open position. The spring 94, the spring loaded, lost motion connection 86 and the adjusting disk 98 of the screw adjustment 88 are preferably so adjusted that the butterfly valve 76 will be fully closed when the bulb 78 is at 32 F. and fully open at 36 F.

The evaporator 34 is supplied with liquid refrigerant from a refrigerating system which includes a compressor 12'3 driven by an electric motor 125 which withdraws evaporated refrigerant from the suction conduit 127 and forwards the compressed refrigerant to the condenser 129 from which the liquid refrigerant flows through a capillary tube restrictor expansion control device 131 to the evaporator 34. The compressor motor 125 is controlled primarily by a snap-acting thermostat switch 133 which is opened and closed in accordance with the temperatures of a thermostat bulb 135 located on the outside of the liner 32 adjacent the upper outlet of the fan 58. The switch 133 is set to close at plus 6 F. and to open at a minus F. Consequently, the evaporator 34 operates considerably below water-freezing temperatures.

During the initial operation of the refrigerator the evaporator 34 will condense water out of the air. This condensed water will flow rearwardly over the bottom 38 of the liner 32 until it reaches the rear edge thereof and will flow down onto the screen 74 and by reason of the capillary attraction of the screen will fill the open spaces of the screen with water. As indicated in FIG- URES 2 and 6, the screen 74 is cooled by a loop 137 of refrigerant tubing which is in contact with the screen and which is located in the refrigerating system between the outlet of the evaporator 34 and the suction line 127. Consequently, the operation of the refrigerating system will cool the screen and the water thereon to belowfreezing temperatures causing the screen to be closed by the frozen condensed water therein. During defrosting periods the defrost water will likewise flow over the screen and fill the open spaces thereof and when frozen will close the screen during the subsequent refrigeration cycle. This prevents the use of the by-pass opening during normal refrigeration operation so that all of the discharge from the fan 58 will go either through the upper blower outlet 64 to the below-freezing compartment 26 or the lower blower outlet 66 to the above-freezing compartment 28.

According to my invention, I initiate a defrost cycle when the frost builds up in front of the evaporator 34 until it reaches the thermostat bulb 139. This bulb 139 extends directly across the bottom 38 of the liner 32 immediately in front of theevap'orator 34. However, to avoid too frequent defrosting and to assure there is a substantial amount of frost deposited on the evaporator 34 before a defrost cycle is begun, I provide a small electric heater 141 between the evaporator 34 and the bulb 139. This heater 141 is energized during each operation of the compressor motor by being connected in parallel therewith as indicated in FIGURE 5. The thermostat bulb 139 connects through the bellows operated snap-action mechanism 133 with the double-throw switch 145. This switch is set so that the contact remains in its lower refrigerating position connecting the supply conductor 147 through the switch 133 with the compressor motor'125 and the heater 141 as long as the temperature of the bulb 139 remains above minus 45 F. The fan motor 60 is connected directly across the supply conductors 147 and 149. The second terminal of the compression motor 125 and the heater 141 are connected directly to the supply conductor 149.

When sufficient frost and ice is built up in front of the evaporator 34 to reach and contact and cool the thermostat bulb 139 below minus 45 F., the bellows and snap-action mechanism 143 will move the doublethrow contact 145 from the lower to the upper position 50. In the upper position the contact 145 will connect the supply conductor 147 with a small heater 151 located immediately adjacent the air damper bulb 78 and a de frost heater 153 connected in series with the heater 151 and connected at its other terminal with the supply conductor 149. The defroster heater 153 is of the inexpensive bare nickel chromium wire type mounted upon the insulator supports 155 directly adjacent the screen 74 as shown in FIGURE 2. The energization of the heater 153 quickly melts the frozen condensed moisture or frozen defrost water upon the screen 74 thereby opening the by-pass opening or passage between the front part of the discharge portion 66 and the passage 50 leading through the opening 44 to the evaporator space 40 at the front of the evaporator 34. Since the fan motor 60 remains in operation, this provides a circulation of warm air through the evaporator 34 and the shroud 54 through the inlet 56 to the fan 58.

The energization of the heater 151 raises the temperature of the bulb 78 to about 46 or more. This provides a considerable increase in the pressure in the fluid motor 84 thereby moving the bellows follower 84 further downwardly and compressing the spring provided in the spring loaded lost motion connection 86. The bellows follower 84 is provided with an arm having an aperture through which extends the lower portion of a wire 161 which is provided beneath the extension 151 with an inwardly turned projection 159 which is engaged and pulled downwardly by the abnormal downward movement of the projection 157 and the bellows follower 84. This pulls downwardly thewire 161 which connects to and closes the upper butterfly damper 163 within the outlet 64 of the fan 58 as best indicated in FIGURE 4. This prevents any air from being discharged into the below-freezing compartment 26 during the defrost period. The wire 161 is enclosed in a tube 162 and has a helically coiled portion 165 above the tube 162. Between the coiled portion 165 and the top of the tube 162 there is provided a small compression spring 167 which normally urges the wire 161 upwardly so as to keep the upper butterfly damper 163 normally in the open position. The outlet 64 of the fan 58 is provided with a downwardly extending sleeve portion 169 enclosing the spring 167 and the coiled'portion 165. As indicated in FIGURES 3 and 4, the portions of the passages 68 and 64 within which are located the butterfly dampers 76 and 163 are horizontal for convenience in connection. The arrangement shown in FIGURE 1 is merely diagrammatic so that all of the mechanism can be shown in a single figure.

The spring 121 beneath the adjusting disk 98 has been substituted for a fixed stop so that upon the yielding of the lost motion connection 86 under the increased pressure within the fluid motor 82 and by the additional pressure created in the bulb 78 and the fluid motor 82 by the heater 151, the spring 121 will be collapsed to move the butterfly damper 76 beyond the fully open position to exert a throttling effect during the defrost period so as to force a sufiicient amount of air to flow past the defrost heater 153 and through the bypass screen 74 after the frost and ice have been melted therefrom. The above-freezing compartment 28 however is provided with air cooled by the evaporator 34 during the defrost period which is discharged from the fan 58 and divided by the partition 72 so that a portion flows through the passage 68 past the partially closed valve 76 through the opening 70 into the above-freezing compartment 28. The remaining portion of the air discharged by the fan 58 passes in front of the partition 72 through the screen 74 and carries this warm air heated by the heater 153 through the passage 50 into the evaporator chamber 40 and through the evaporator 34. Some air is also drawn from the above-freezing compartment 28 through the opening 46 and the passage 48 to the passage 50 to provide circulation within the above-freezing compartment during the defrost period. The mass of food within the compartment 26 is sufficient to prevent any substantial rise in temperature during the short defrost period.

The defrost period continues with the switch 145 in the upper position until the bulb 139 reaches a temperature of 37 F. which is sufficient to insure defrosting of the evaporator 34. When this temperature is reached, the bellows and snap-action mechanism 143 will move the double-throw switch 145 from its upper position to its lower position as shown in FIGURE 5. This will deenergize the bulb heater 151 and the defrost heater 153 and will energize the compressor motor 125 to resume refrigeration and will also energize the small bulb heater 141 to restore the system to normal operation for producing and maintaining refrigeration.

While the embodiment of the present invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. Refrigerating apparatus including an evaporator in heat transfer with air for cooling the air and coincidentally condensing moisture from the air, an air duct extending to said evaporator, a screen having capillary properties extending across said air duct, means for collecting condensed moisture from said evaporator and conducting said condensed moisture to said screen, and refrigerant evaporation conduit means extending into intimate heat transfer relation with said screen for freezing the condensed moisture upon said screen to close said air duct.

2. Refrigerating apparatus including an evaporator in heat transfer with air for cooling the air and coincidentally condensing moisture from the air, an air duct extending to said evaporator, a screen having capillary properties extending across said air duct, means for collecting condensed moisture from said evaporator and conducting said condensed moisture to said screen, refrigerant evaporator conduit means extending into intimate heat transfer relation with said screen for freezing the condensed moisture upon said screen to close said air duct, and heating means in heat transfer relation with said screen for melting the frozen moisture to open said air duct.

3. A refrigerator including insulating means enclosing a compartment to be cooled, duct means having inlet means and outlet means communicating with said compartment to be cooled, circulating means for circulating air from said compartment through said inlet means and said duct means and said outlet means, refrigerant evaporator means in said duct means for cooling the circulating air and incidentally accumulating frost, by-pass means providing communication between the part of said duct means between the evaporator means and said outlet means and the part of said duct means between said inlet means and said evaporator means, means for normally closing said by-pass means, a defrost heater in heat transfer with said by-pass means, and defrost control means for opening said by-pass means and for closing the outlet means of said duct means and energizing said heater for causing said circulating means to circulate warm air through said duct means and said evaporator means to defrost said evaporator means.

4. A refrigerator including insulating means enclosing a compartment to be cooled, duct means having inlet means and outlet means communicating with said compartment to be cooled, circulating means for circulating air from said compartment through said inlet means and said duct means and said outlet means, refrigerant evaporator means in said duct means for cooling the circulating air and incidentally accumulating frost, by-pass means providing communication between the part of said duct means between the evaporator means and said outlet means and the part of said duct means between said inlet means and said evaporator means, means for normally closing said by-pass means, a defrost heater in heat transfer with said by-pass means, and means responsive to frost accumulation upon said refrigerant evaporator means for opening said by-pass means and for closing the outlet means of said duct means and energizing said heater for causing said circulating means to circulate warm air through said duct means and said evaporator means to defrost said evaporator means.

5. A refrigerator including insulating means enclosing separate below and above freezing compartments insulated from each other, duct means having inlet means and outlet means communicating with said below and above freezing compartments, circulating means for circulating air from said compartments tl n'ough said inlet means and said duct means and said outlet means, refrigerant evaporator means in said duct means between said inlet means and said outlet means for cooling the circulating air and incidentally accumulating frost, by-pass means providing communication between the part of said duct means between the evaporator means and said outlet means and the part of said duct means between said inlet means and said evaporator means, means for normally closing said by-pass means, a defrost heater in heat transfer with said by-pass means, and defrost control means for opening said by-pass means and for closing the outlet means of said duct means and energizing said heater for causing said circulating means to circulate warm air through said duct means and said evaporator means to defrost said evaporator means.

6. A refrigerator including insulating means enclosing separate below and above freezing compartments insulated from each other, duct means having dual inlet means and dual outlet means communicating separately with said below and above freezing compartments, circulating means for circulating air from said compartments through said inlet means and said duct means and said outlet means, refrigerant evaporator means in said duct means between said inlet means and said outlet means for cooling the circulating air and incidentally accumulating frost, temperature responsive valve means responsive to the temperature of the above freezing compartment for normally controlling the flow of said cooled air from the portion of the dual outlet means communicating with said above freezing compartment to maintain said above freezing compartment at above freezing refrigeration temperatures, by-pass means providing communication between the part of said duct means between the evaporator means and said outlet means and the part of said duct means between said inlet means and said evaporator means, means for normally closing said by-pass means, a defrost heater in heat transfer with said by-pass means, and defrost control means for operating said valve means to '7 closed position and for closing the other portion of said dual outlet means and opening said by-pass means and energizing said heater-for causing said circulating means to circulate warm air through said duct means and said evaporator means to defrost said evaporator means.

7. A refrigerator including insulating means enclosing separate below and above freezing compartments insulated from each other, duct means having dual inlet means and dual outlet means communicating separately with said below and above freezing compartments, circulating means for circulating air from said compartments through said inlet means and said duct means and said outlet means, refrigerant evaporator means in said duct means between said inlet means and said outlet means for cooling the circulating air and incidentally accumulating frost, temperature responsive valve means responsive to the temperature of the above freezing compartment for normally controlling the flow of said cooled air from the portion of the dual outlet means communicating with said above freezing compartment to maintain said above freezing compartment at above freezing refrigeration temperatures, by-pass means providing communication between the part of said duct means between the evaporator means and said outlet means and the part of said duct means between said inlet means and 8 rator means to defrost said evaporator means, said temperature responsive valve means when heatedalso having means effective to operate said normally open valve means to closed position.

8. In combination, first and second ducts, a first butterfly damper in said first duct, a second damper in said second duct, fluid pressure means operably connected to said first damper for gradually opening said first damper and continuing the movement beyond the fully open position to close the damper, and lost motion connecting means connecting said fluid pressure means and said second damper in response to a predetermined movement of said first damper beyond the fully open position for operating said second damper.

9. In combination, first and second ducts, a first butterfiy damper in said first duct, a second damper in said second duct, temperature responsive means operably connected to said first damper for gradually Opening said first damper and continuing the movement beyond the fully open position to close the damper, and lost motion connection means connecting said temperature responsive means and said second damper in response to a predetermined movement of said first damper beyond the fully open position for operating said second damper to the closed position.

References Cited in the file of this patent UNITED STATES PATENTS 1,727,777 Juneau Sept. 10, 1929 2,346,287 Borgerd Apr. 11, 1944 2,829,505 Oates Apr. 8, 1958 2,907,180 Mann Oct. 6, 1959 2,997,857 Clark Aug. 29, 1961 3,050,956 Mann Aug. 28, 1962 

1. REFRIGERATING APPARATUS INCLUDING AN EVAPORATOR IN HEAT TRANSFER WITH AIR FOR COOLING THE AIR AND COINCIDENTALLY CONDENSING MOISTURE FROM THE AIR, AN AIR DUCT EXTENDING TO SAID EVAPORATOR, A SCREEN HAVING CAPILLARY PROPERTIES EXTENDING ACROSS SAID AIR DUCT, MEANS FOR COLLECTING CONDENSED MOISTURE FROM SAID EVAPORATOR AND CONDUCTING SAID CONDENSED MOISTURE TO SAID SCREEN, AND REFRIGERANT EVAPORATION CONDUIT MEANS EXTENDING INTO INTIMATE HEAT TRANSFER RELATION WITH SAID SCREEN FOR FREEZING THE CONDENSED MOISTURE UPON SAID SCREEN TO CLOSE SAID AIR DUCT. 